The invention relates generally to compositions comprising starch and biogums and more specifically to stable high solids starch/biogum compositions which are readily pumpable and flowable and characterized by stable viscosity. In particular, the invention relates to highly stable compositions comprising depolymerized starch and gellan gum.
The invention also relates to compositions for paper manufacturing including additives for the wet-end of a paper manufacturing process as well as for other aspects of paper and paperboard manufacture.
Starch is the most widely used additive in the paper industry. It is mainly used in paper to provide dry strength to the final paper or board product. It is used in three primary areas of the paper making process; the size press which uses about 65% of the total starch, the wet-end which uses about 20% of the total starch and as a coating binder which uses about 15% of the total starch used in the paper making process.
There are notable differences in the starches used in the three areas. The wet-end uses the highest molecular weight starch (usually native molecular weight, i.e. not thinned), and the wet-end starches are almost exclusively cationic starches. Size press starches are always reduced in molecular weight to allow them to be run at higher solids and lower viscosity. They may be cationic in nature but are normally enzyme or persulfate converted, oxidized or hydroxyl ethylated starches. Coating starches are usually further reduced in molecular weight and again (with few exceptions) are not cationic. Like size press starches, they are normally oxidized or hydroxyl ethylated, with some enzyme converted or persulfate converted starches being used.
Although a significant amount of the total starch used in paper and board manufacture is added to the wet-end of the paper or board machine, it is still much less than that used at the size press. This is in spite of the fact that starch added in the wet-end is much more efficient at increasing the strength of the paper or board (particularly heavy weight papers and board). Starch is more efficient in the wet-end because it is more evenly distributed throughout the sheet whereas starch applied at a size press starch has difficulty penetrating to the center of the sheet. In addition, since the size press starches are lower molecular weight, they do not add strength as efficiently as the higher molecular weight wet-end starches. Finally, the single biggest reason that the wet-end is better than the size press for adding starch is that the sheet is rewetted in the size press and must be re-dried after going through the size press. This means that the paper machine must have additional dryer capacity and there is an energy cost to this additional drying.
The reason for the high molecular weight of wet-end starches is that strength development is thought to occur by a bridging of the wood fibers by the starch molecules. Since the starch molecules are placed in a very dilute environment with the wood fibers, higher molecular weight starches are thought to be better retained and exhibit higher activity (better bonding) than lower molecular weight starch molecules. This has shown to be the case in conventional wet-end systems when comparing a cationic potato starch (which has higher average molecular weight) to a cationic dent corn starch. On a dry lb/ton comparison basis, the potato starch will generally outperform the corn starch. The reason potato starch is not more commonly used in the paper industry is more economical (cost per pound) than performance.
The limiting factor in the use of conventional wet-end cationic starches is a tendency to reduce drainage and retention at high dosages. For high charge cationic starches (which can work very well, especially in dirty, recycled furnishes) the creation of foam at high dosages limits their use. There is a need, therefore, for a starch material that gives high strength, improves (or does not interfere with) drainage and retention and can be used at higher dosages for difficult higher weight papers and boards, particularly in recycled fiber furnishes.
There are many other chemicals used in the wet-end of the paper machine. These would include (but are not limited to): wet strength resins (cationic polyamide-epichlorohydrin resins), polyacrylamide dry strength resins, polyacrylamide-polyacrylic acid anionic resins, ASA and AKD sizing compounds, colloidal silica, CaCO3 fillers (TiO2, clay, silica), CMC, retention aids, and in certain cases alum and rosin sizing (used mostly in non alkaline papermaking systems). All of these materials interact with each other and with the fiber and (in the case of recycled papers and paperboard) other substances (contaminants) that comes along with the recycled fiber. Any new material added to a paper making system (especially if the new material is added to a recycled fiber system) must have a positive interaction with most if not all of the substances and chemicals listed above.
Combinations of starches and biogums are well known in the art of paper manufacturing. For example, Winston, Jr. et al., U.S. Pat. No. 5,112,445 reports that a combination of gellan gum and starch demonstrates enhanced film formation on the surface of a coated paper sheet. The compositions disclosed by Winston, Jr. comprise a hydroxyethyl starch ether in combination with a low-acyl gellan gum at weight ratios ranging from 80:1 to 160:1. Winston, Jr. does not teach starch/gellan gum ratios that enhance internal strength nor that affect size pickup levels. Nevertheless, there remains a desire in the art for improved surface sizing compositions providing improved properties.
Rooff et al., U.S. Pat. No. 6,290,814, the disclosure of which is hereby incorporated by reference, discloses a method for sizing paper which comprises the step of coating paper with a composition comprising gellan gum and a derivatized starch wherein the derivatized starch and the gellan gum are present at a weight ratio of from 300:1 to 1000:1. Also provided by the invention are improved papers adapted for ink jet printing characterized by an ash content of from 5% to 30% by weight, permeability characterized by a Hercules Size Test (HST) score in the range of over 200 seconds and treated with a surface size comprising gellan gum and a derivatized starch wherein the derivatized starch and the gellan gum are present at a weight ratio of from 100:1 to 1000.
Werner et al., U.S. Pat. No. 2,949,397 discloses incorporating loading agents or fillers, together with an organic colloid material (locust bean gum, guar gum, konjak) into paper in such a way that the particles of filler are wholly or partly coated with the organic colloid material. As stated in the patent, the particles of mineral filler do not form stable suspensions with the colloidal dispersions of the (locust bean gum, guar gum, konjak or substituted versions thereof) and must be kept agitated.
Sundén et al., U.S. Pat. No. 4,710,270 describes a process for combining a “swollen” cationic starch with a polysaccharide acid of high charge density such as CMC and alginates. The cationic starch and CMC or alginate is then mixed with a polyaluminum citrate complex and blended with clay or chalk to form an envelope around the clay or chalk. These amphoteric mucous compounds are then mixed with the filler slurry and added to the wet-end of a paper machine. While these amphoteric mucous compounds do show improved retention and strength, they are not practical to make at a commercial level since they are low solids, unstable mixtures.
Clare et al., U.S. Pat. No. 5,079,348 describes a combination of starch, a biogum and an alginate for use on the size press of a paper machine. Again, the mixtures are low solids (8-10%) and are made to be used at a temperature of 100-160° F. Taggart et al., U.S. Pat. No. 5,104,487 describes a process for adding a cationic starch and a biogum to the cellulosic fibers in a normal paper machine furnish, Taggart teaches that the starch and biogum must be added separately to the furnish to achieve uniform distribution and maximum strength. Taggart also teaches use of relatively high levels of gum relative to the weight of cationic starch.
Fairchild, U.S. Pat. No. 5,458,679 teaches treating inorganic materials such as calcium carbonate, clay, TiO2, talc and the like with an anionic polysaccharide such as anionic guar or xanthan gum. The anionic polysaccharide is mixed with the inorganic material prior to addition to the cellulosic fibers in the pulp slurry. They do not teach making a stable, high solids blend with these materials. Nor do they teach that any of these blends will have an effect on the retention and drainage of the furnish when used on a paper machine.
As seen by the prior patents, a need exists for a high solids, stable, pumpable/flowable combination of biogum and starch that is cost effective and ready to use in the wet-end of a paper machine and not only provides strength, but also improves drainage and retention.
Of interest to the present invention is the disclosure of Black, U.S. Pat. No. 4,014,743 which discloses a method for continuous enzyme liquefaction (thinning) of starch to produce high solids dispersions of cooked starch and water. The process consists of (a) mixing a granular starch with water; (b) adding an enzyme (usually a bacterial alpha-amylase) to the composition; (c) adding the composition of step (b) to a stirred and heated tank on a continuous basis such that the peak cook viscosity in the stirred tank of the cooked and thinned paste is lower than would be possible if the entire mixture of (b) was heated and cooked as one batch. The cooked and thinned paste of (c) is then passed (after a certain start-up period) through a jet cooker to deactivate the enzyme and finish dispersing the starch molecules. This cook process allows higher solids of the cooked paste due to the fact that the maximum viscosity of the cooked paste at any point in the cook process (even at much higher solids) is much lower than would seen if the entire batch was cooked at once.
Also of interest to the present invention is the disclosure of Skuratowicz et al. U.S. 2009/0142812 which is directed to methods of making high molecular weight reduced viscosity starch pastes by (a) mixing a granular starch with water; (b) adding one or more starch hydrolyzing enzymes to the composition; (c) jet cooking the composition of step (b) in a first jet-cooker to a temperature of from 160° F. to 210° F.; (maintain the composition for a specified hold time; (e) following step (d) jet-cooking the composition in a second jet-cooker to a temperature to a temperature from about 250° F. to 300° F. and recovering a hydrolyzed starch paste wherein at least 20% of the polymers in the paste have a molecular weight from 10,000 to 200,000 Daltons and fewer than 5% of the polymers have a molecular weight less than 10,000 Daltons.
Also of interest to the invention is the use of biological gums such as guar in applications such as in water treatment for example in the manufacture of flocculants and as “muds” for oil drilling and as proppants and hydraulic fracturing fluids the increased use of which has resulted in shortages and significant price increases for gums such as guar.
Accordingly, there remains a need for compositions to provide improved physical properties to paper and paperboard as well as for other uses.